This invention relates to a process for preparation of chloroprene monomer in which quaternary ammonium phase transfer catalyst is removed from the crude product by treatment with an oxy acid.
Chloroprene (2-chlorobutadiene-1,3) is an important monomer used in the manufacture of a number of synthetic elastomers. It is normally prepared by dehydrochlorination of 3,4-dichlorobutene-1 ("DCB") with aqueous alkali, for example sodium hydroxide. U.S. Pat. No. 3,981,937, Campbell et al., discloses a catalytic process for carrying out the dehydrochlorination in the presence of a quaternary ammonium salt catalyst.
In one variant of the Campbell et al. process, DCB, aqueous alkali, and the catalyst are introduced into one or more agitated reaction vessels and allowed to react at moderately elevated temperature (e.g. 50.degree.-70.degree. C.) until the DCB is substantially completely dehydrochlorinated. The reactor effluent contains the chloroprene product, excess aqueous alkali, brine formed in the process, the catalyst, and various organic byproducts. Chloroprene is recovered from the effluent by steam-stripping.
U.S. Pat. No. 4,605,800 discloses an improvement in the process for manufacture of chloroprene. The effluent from the dehydrochlorination reactor is separated into phases, and the organic phase is steam-stripped at low temperature (below about 80.degree. C.) to recover chloroprene product, while the steam stripper heels (containing the catalyst) are returned to the dehydrochlorination reactor. The organic phase may be treated with an acid such as, for example, acetic acid or sulfuric acid, to neutralize residual alkali prior to the steam stripping step.
Although the use of quaternary ammonium salt catalysts results in the attainment of high yields in the above-described dehydrochlorination processes, the use of these compounds is associated with certain disadvantages. For example, the presence of the catalyst causes corrosion of equipment used in recovery of chloroprene from the organic phase. In addition, the presence of catalyst in the organic phase results in entrainment of water and brine in that phase due to the surfactant properties of the catalyst.